Rabbits – Okunoshima, Japan

Another Japanese island, another island overrun by critters! This time it’s Okunoshima, a small island in the Inland Sea whose main feature is a 740ft tall hydroelectric pylon. Okunoshima harbors a darker side as well: it hosted the country’s main poison gas production facility from the late 1920s.

After World War II ended, American occupation forces disabled the gas factories and disposed of any stored poison gas. The island was redeveloped as a park and in 1971 rabbits were released to roam freely, while a Poison Gas Museum was established in 1988 to educate visitors about the once-secret poison gas program.

Word of Okunoshima’s friendly and abundant population of rabbits has spread and these days the island is the focus of rabbit-based tourism. The rabbits themselves do not appear to be adversely affecting the island’s plant and animal life, and unlike other places where rabbits have been introduced, Okunoshima’s rabbits are protected from hunting.

Mice – Gough Island

Gough Island is about as far away from dry land as one can get. This South Atlantic speck measures just 13 km (8.1 mi) by 7 km (4.3 mi) and sits roughly 2,700 km (1,700 mi) from South Africa’s Cape of Good Hope. Isolated as it is, Gough Island has a long history of human visitation going back to the year 1505 and during one of those visits, common house mice escaped from one of the landing ships. The humans didn’t stay but the mice did.

Unchecked by predators and unhindered by seabird chicks that, while massively outweighing them, had no way to defend themselves, Gough Island’s mice ran amok… and as time passed, their average size increased as well. Attacking chicks in their burrows during the night, gangs of mice make short work of many threatened species and in total their population has ballooned to more than 700,000. Rodents of unusual size and numbers!

Crabs – Christmas Island

It’s beginning to look a lot like Christmas – at least, the island by that name annually gets a huge splash of red to go along with its greenery, and it usually happens in November. The scarlet splash comes by virtue of the Red Crab, native to Christmas Island and numbering in the tens of millions. Compare that to the human population of only 1,500 or so, and you’ve got the makings of an annual overrunning with a capital O!

Not only do the Red Crabs migrate from their inland rainforest burrows to the sea, their offspring perform the feat in reverse creating difficulties for pedestrians, drivers and trains (until the railway was closed in 1987).

Curiously, there is no notable mention of the crabs in chronicles left by early colonists. It’s possible the extinction of two types of native rat in the early 20th century may have allowed the Christmas Island crab population to explode. Nature finds a way, as always: invasive yellow “crazy ants” from Africa are blamed for a sharp reduction in crab numbers noted in recent years.